Catalog - Lazarusina lazarusi

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Lazarusina lazarusi

Citation: Lazurusina lazurusi Georgescu 2013

Type specimens: Holotype: Specimen ECO–050–35. Paratypes: Specimens ECO–050–30 to 34 and ECO–050–36 to 38.

Type sample (& lithostrat): white chalk, Sample 62–463–8–1, 50–52

Type age (chronostrat): Lower Maastrichtian (upper Gansserina gansseri Biozone)

Type locality: Type locality: DSDP Site 463 (Mid–Pacific Mountains, Pacific Ocean), geographic coordinates: 21° 01’N and 170°40.07’ E.

Type repository: Ehrenberg Collection,Museum of Natural History Museum, Berlin

Diagnosis: Lazarusina with early planispiral coil.

Description: Test holohelicid; proloculus is spherical, situated in the central early portion of the test and with a diameter of 0.010–0.013 mm. Early stage consists commonly of four to five subglobular chambers, rarely six, which are arranged forming a whorl that completely surrounds the proloculus. Adult stage consists of 7 to 10 globular chambers with gradual size increase, which are alternately added with respect to the test growth axis and overlap at various rates. Sutures in the test adult portion are distinct and depressed, straight to slightly curved and perpendicular or slightly oblique to the test growth axis; sutures of the early planispiral stage are often indistinct. Test is symmetrical in edge view, with a broad and simple periphery. Aperture is a medium high wide arch situated at the base of the test last–formed chamber. Two symmetrically developed narrow subtriangular metaflanges border the aperture on each test side. Chamber surface ornamentation consists of more or less continuous leptocostae, which are parallel to the test growth axis and periphery and have a thickness of 0.0035–0.0054 mm; ornamentation is more prominent over the test early portion due to the addition of successive calcite layers during the ontogenetic development. A periapertural pustulose area consisting of dome–like or irregular in shape pustules 0.0012–0.0026 mm in diameter or maximum dimension respectively is developed over the chamber anterior face at least in the adult stage. Test wall is calcitic, hyaline, simple and perforate; pores are circular, with a diameter of 0.0013–0.0023 mm and are situated in the space between the leptocostae, rarely interrupting them.

Holotype dimensions: Length: L=0.2847 mm; width: W=0.1892 mm; thickness: T=0.1425 mm; diameter of early planispiral stage: Deps=0.0634 mm; W/L=0.665; T/L=0.501; Deps/L=0.223. Paratype dimensions: L=0.2601–0.3000 mm; W=0.1879– 0.2580; T=0.1400–0.1862 mm; Deps=0.0486–0.0720 mm; W/ L=0.665–0.885; T/L=0.466–0.639; Deps/L=0.162–0.259. Ranges based on the average measurements of 15 specimens: holotype, seven paratypes and seven hypotypes.

named after Dr. David Lazarus (Museum of Natural History, Berlin).

Remarks: Ehrenberg (1854) illustrated specimens he assigned to Spiroplecta americana (renamed herein S. clarae) from two geographic regions of the USA: Missouri River Basin (plate 32, part I) and Mississippi (plate 32, part 2). The specimen illustrated from the Mississippi region is lost. Re–examination of the bulk samples and the planktic foraminiferal assemblages they yielded indicates that the Missouri specimens were collected from the Fort Hays Limestone Member of the Niobrara Formation (Santonian) whereas those from Mississippi from the Ripley Formation (late Campanian). The two species with holohelicid tests, S. clarae and L. lazarusi can be easily recognized: the former is distinctly compressed and occasionally has pinched last–formed chamber and the latter is globular–chambered throughout. They were considered conspecific by Ehrenberg (1854) most likely because test thickness could not be assessed in the specimens from the mica disks. Lazarusina lazarusi differs from its ancestor L. globocarinata mainly by having holohelicid rather than ahelicid test; pore diameter increases from the ancestral L. globocarinata (0.0010–0.0017 mm) to the descendant L. lazarusi (0.0013–0.0023 mm).

References:

Georgescu, M. D. (2013c). Revised evolutionary systematics of the Cretaceous planktic foraminifera described by C.G. Ehrenberg. Micropaleontology. 59: 1-48. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Lazurusina lazurusi Georgescu 2013

Lazarusina lazarusi

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